U.S. Pat. No. 4,705,919, Dhawan, discloses an electrostatic pattern coupled digitizer comprised of a tablet having three coplanar electrodes, including two differently shaped sawtooth configured electrodes and a third electrode covering the remainder of the surface of the tablet. Signals are selectively applied to the electrodes, and the position of a cursor electrostatically coupled thereto is calculated from ratiometric measurements of the signals coupled to the cursor. Alternatively, the signals may be applied to the cursor, with the ratiometric measurements being taken of the signals coupled to the tablet electrodes.
While the above device provides the desired position related output, it requires the use of a relatively complicated precisely shaped electrode pattern.